Regulator for amplifiers



April 19, 1932.

0. M. G. DE L'HARPE REGULATOR FOR AMPLIFIERS Filed Jan. 15, 1926 INVENTOR OLUVIER ME. de 1'HARPE ATTORNEY Patented Apr. 19, 1932 UNITED STATES PATENT OFFICE OLLIVIER MARIE FBANCAISE RADIO ELEC1RIQ''E, OIE PARIS, FRANCE BEGULATOR FOR AMPLIFIERS Application filer] J'anuary 15, 1926,

The invention concerns anamplifying sys tem and has for its principal object to. provide such a system in which the amplification factor shall change inversely with respect to the power applied toits input circuit.

Another objct of the invention is to provide such a system in which the amplification Will vary in inverse ratio t0 persistmg changes in the applied power but Will not so vary on instantaneous changes.

Still another object of the invention is to provide such a system in which an amplify ing device'has a resistance in its input circuit Which Will automatically increase in value with increase of current.

Still another object of the invention is to provide an amplifying device having a resistance in its input circuit which Will vary in value directly with the amount of current fiowing therethrougb but whose variations Will be subj ect to an appreciable time lag.

The invention has been found particularly useful in connection with automatic regulators for amplifiers used in connection with modulators in radio transmitting stations, although it should be understood that it is not limited to this use. In broadcasting programs from such stations it has been the cus tom t0 manually control the amplification to improve the quality of the music or other material being broadcasted. This is necessary on account of the diferent Ways in which dif ferent parts of a musical selection, for example, are rendered. If certain portions of a selection are played Witb greater vigor thereby impressing an excessive volume of sound on the microphone, an affect known as blast ing results causing a very disagreeable noise due to the overloading of the apparatus. On the other hand, if portions of the music are being plaed softly, it may be very difiicult for operators of broadcast receivers to hear them distinctly. In the former.case, the amplification is decreased in the transmitting station and in the latter case it is increased by the proper amoun This volume regulation or monitoring is not altogether satiS. factory because the operator naturally only corrects the undesirable features in the rendition of the program after they have beguri to be apparent.

Serial No. 81,399, and in France .Iu1y 22, 1925.

Under the present system I provide for automatic monitoring. This may be accomplished in a multi-stage amplifier by transferring the current to be amplified from one stage to the s'ucceeding one across a resistance which Will increase in value with the intensity of current fiovving therethrough. It has been found that an incandescent lamp with a metallic filament and of suitable rat-- ing can be used advantageously for such a resistance. This arrangement owing to the' increase in resistance when large currents are flowing automatically reduces the amplification for large amounts of power and increases it for small amounts of power. A further advantage of such a resistance resides in the fact that this resistance does not change instantaneously with increase of current but only after an appreciab le time interval.

This, as will be explained hereinafter, is an important feature of the invention.

The invention is illustrated by way of example in the accomp anying drawing in which the single figure represents a diagrammatic circuit arrangement according to. the invention.

Referring tothe drawing a two stage ain plifier is shown consisting of two three eleetrode vacuum tubes L and L, connected together in cascade. The cathodes of these tubes may be connected in parallel and enerr gized from a common source A. A common plate battery B is provided to supply the plate current of both tubes. The current to be amplified is applied to the terminals 1, 2 and transferred to the input circuit of the tubeL across the transformer T The plate circuit of this tube is connected to the bat tery B through a resistance R and the primary of a transformer V T is connected through a condenser C to a point between the resistance It and the plate of the tube L the other terminal of this transformer primary being grounded as at G. The amplified current in the plate circuit of the tube L is transferred to the input circuit of the tube L by means of a transformer T whose secondary is connected across the filament and grid of the tube L and may be shunted by a res1stance R if desired. The primary of the transformer T is connected to the secondary of the transformer T a resistance R whose funotion will be explained in detail hereinafter being inserted in series in the circuit. The amplified current in the plate circuit of the tube L may be used to energize any desircd device, shown in the present case as an inductance Y. This inductance may be any desired apparatus which it is desired to operate. It may, on the other hand, be the primary of an additional transformer leading to other stages of amplification.

The resistance R which in efi'ect is in series in the circuit connecting the tube L to the tube L is so chosen that it Will increase with the intensity of the current which traverses it. As explained above an incandescent lamp with a metallic filament can advantageously be used for this resistance. The eifect of this resistance can be best explained by a simple numerical example. It may be chosen so that if E designates the voltage across the secondary of the transformer T E the voltage across the primary of the transformer T and I the current in the resistance R the following values Will be obtained:

E=l volt E:O. 5 volts I 1 ampere E=100 volts E=5 Volts I=l0 amperes t Will be seen that with such an arrangement the amplifying power of the system uill be ten times greater for small amplitutes than for large ones. It is, of course, possible to obtain an even greater variation in amplifying power by suitably choosing the resistance R It is understood that the number of stages of the amplifier can be as desired and that the method of connecting between stages is adapted to wide variations. Moreover, the arrangement can be applied if desired,between several successive stages of a multistage amplifier or only between two particular stages of such an amplifier. The two stage amplifier illustrated with its particular connections is given merely by way of example.

It should be noted that a very important advantage of the device results from the calorific inertia of the metallic resistance R WhiCli Will lie of the order of several bundredths of a second. OWing to this inertia, a variation of the resistance is not perceptible in the course of a period of the order of a single musical note. This eliminates all danger of distortion from cleformation of the wave produced by a succession of musical notes. Such a distortion would appear, of course, if use were made of a resistance which would vary instantaneously, such resistances, for example, as can be formed from three electrode vacuum tubes. On the other hand, the variation of the resistance of the metallic filament used in the present case is subject to a time lag so that the device Will change its amplification factor only if several notes in succession are played more softly or more loudly than the passage immediately proceed ing them. This system has been found to be incomparably superior to the usual manual systems of regulation in which an operator Watches a measuring instrument indicating the intensity at the output of the amplifier and increases or decreases the volume by manipulating suitable controls. In such a system the operator 2ilmost invariably corrects the faults in the reproduction of sounds only after they li ave become apparent in the broadcasting. Under the present system, however, While the resistance does not change quickly enough to cause distortion in the musical notes it, nevertheless, changes so quickly that too much or too little volume is autom atically corrected before it becomes apparentto listeners.

While I havedisclosed my invention in connection with a particular circuit arrangement, it Will be obvious to those skilled in the art that it is adapted to many modifications and to many different uses. I intend to be limited, theref0re, only as indicated by the scope of the following claims Claims 1. An amplifying system comprising an amplifying device and a resistance having a positive temperature coefficient connected therewith, said resistances being so connected with the device that it varies the amplification factor of the alternating current componet in inverse ratio to the applied energy and additional means to prevent the direct current component from fiowing through said resistance.

2. A multi-stage amplifier comprising a plurality of connccted amplifying devices and means including an. element having a positive temperature coefficient of resistance connected between two successive stages, said means being so connected that it varies the amplification of the alternating current conaponent across said stages inversely tothe amount of energy applied thereto and additional means to prevent the direct eurent component from flovving through said resistance element.

3. A multi-stage amplifier comprising a plurality of connected amplifying devices and a resistance possessing a positive temperature ooefiicient of a predetermined valve connected between tvro successive stages, said resistance being se connected that it varies in value xvith persistent variation in the cur rent therethrough for varying the amplification across said stages in accordance with the energy applied thereto and additional means for preventing the flow of direct current through said resistance.

4. A multi-stage amplifier comprising a plurality of tubes connected in cascade, a resistance connected in series, between two adjacent tubes, with an element coupled to the anode circuit of one of said adjacent tubes the first transformer,

therethrough vvhereby the amplification:

across said tubes varies inversely to the ap-- persisting changes in the but not for instantaneous changes and additional means to prevent the= flow of direct current through said resistance.. frequency amplifying sys-- an aperiodic link circuit successive stages, and;

plied energy for amount of energy,

5. In an audio tem, in combination, connected between tvvo means having a positive temperature coeflicient of resistance included in said link circuit, vvhereby the amplification factor of the alternating current component varies inversely with the appliecl energy to be amplified.

6. In a two-Stage audio frequency amplify ing system, the combination with an aperiodic link circuit connected between said stages, of a resistance having a positive tem perature coefficient in said link circuit of such value that increase in input energy Will efect a decrease in the amplification factor cf said system.

7. A multistage amplifying system, comprising a link circuit connected between successive stages and a resistance having a positive temperature coefficient in each of said link circuits of such value that increase in input energy Will efi'ect a decrease in the amplification factor of said system.

8. In a two-stage audio frequency amplifying system, in combination, an aperiodic link circuit connected between said stages, a resistance having a positive temperature coeificient in said lin]: circuit vvhereby blasting is electively eliminated, and a clamping resistance connected in the input circuit of the last stage.

9. A multi-stage amplifier comprising a plurality of cascade connected vacuum tube.

amplifiers, a resistance connected between successive stages, said resistance changing in value vvith variations of current therethrough, vvhereby the degree of amplification across said amplifiers varies inversely to the applied energy for persisting changes in the amount of energy changes.

10. In an audio frequency amplifying system, a transformer, a resistance, a second transformer, means for utilizing energy, and means to furnish energy ,to the primary of the secondary of the first transformer being connected in serieS and forming a closed circuit with the resistance, and with the primary of the second transformer, transformer ing means.

supplying energy to the utiliz- OLLIVIER MARIE GUSTAVE de lllARPII.

but not for instantaneous the secondary of the second" 

